In the course of manufacturing parts, it is sometimes necessary to package the partially assembled work piece for shipment to another location for further assembly or other manufacturing operations. The manufacturer is then faced with the need to unpackage the parts, unload the parts, perform the needed operation, and then repackage the shipping containers (dunnage) for return. A typical method of packaging is to place the parts in trays arranged in rows and columns and stack the trays in layers. The trays may be molded plastic shaped to accommodate the particular part or work piece. The stack of trays is then loaded on a shipping pallet and secured for shipment. At the destination, the stack must be removed from the pallet and each tray separated from the stack. The parts are then unloaded from the individual trays and moved into the manufacturing line. The empty trays must be stacked and placed back on the pallet for future use.
An example of the type of parts packaged in this manner is automotive parts such as pistons. A particular manufacturing operation is the assembly of the pistons with the piston rings. In this example the pistons are loaded in trays which may have ten rows of recesses of nine in a row. As many as 14 full trays may be stacked on a pallet. Each stack can weigh in excess of a ton. The handling of such dunnage requires machinery of considerable size. It is, therefore, desirable to reduce the size of the handling apparatus to reduce the shop floor area required.
Prior art systems such as shown in U.S. Pat. No. 4,946,340, use the most obvious approach, namely to destack the trays starting at the top and working downward. This requires a high frame extending well above the height of the stack because the apparatus which unloads the parts from the tray must operate above the entire stack. The path of this system leaves the empty pallet to be handled last. Since the transport of the pallet to the stacking zone must be accomplished before any of the empty trays can be restacked, a costly delay is caused in the manufacturing process.
The system of the '340 patent is approximately ten feet in height and is controlled from a platform at least five feet off the shop floor. It is the purpose of this invention to provide a dunnage handling system of reduced height and area while eliminating costly delays in handling the stacks. The part unloading system of this invention operates at a height of only one tray above the associated conveyors.